Study On The Solvent Fractionation Of Enzymatic Hydrolysis Lignin And Methylene Blue Adsorption By Its Fractions

The annual yield of lignin,the most abundant natural aromatic compounds in nature,is very large.Due to the structure complexity and broad dispersity of the lignin molecular weight,the application of lignin in industry was limited.However,lignin can be fractionated by molecular weight and performance,and further used according to its characteristic.The corn stalk enzymatic hydrolysis lignin(EHL)as raw material was fractionated by two methods,glycerol-ethanol aqueous solution and ethanol aqueous solution respectively in this paper.The three lignin fractions(Fl,F2 and F3)can be obtained by the two fractional methods.The study found that the two fractionation methods also had purification function for lignin and lignin fractions.And the molecular weight and dispersion of lignin were reduced in the fractionation process by GPC analysis.According to the subsequent FTIR,NMR and Py-GC/MS analyses,it found that the three lignin fractions compared with EHL mainly had changes in molecular weight,and the chemical structure did not appear obvious change.These can prove that the fractional methods did not destroy the structure of lignin.However,in addition to molecular weight of lignin,there was also a difference between F1,F2 and F3 in phenolic acids,S and G type content of lignin.The content of phenolic acids and S type in F1 is higher than that of F2 and F3,while the content of G type had opposite tendency.The three fractions and EHL obtained by water-ethanol solvent were applied to adsorb methylene blue solution.The adsorption effect were EF3>EF2>EHL>EF1,namely large molecular weight of lignin on the adsorption effect of methylene blue solution was the best,and the methylene blue adsorption unit of EF3 was 415 mg/g.The kinetic model for blue was fit pseudo-second-order kinetic models,and the EF3 adsorption of methylene accorded with Langmuir adsorption isotherm.The FTIR spectra of lignin and adsorbed methylene blue were analysed and found that the characteristic peaks in spectra were corresponed to methylene blue.Thus this could prove that the lignin adsorbed methylene blue.Through the analysis of the Zeta potential,particle size,specific surface area,SEM and EDS results,these proved the EF3 of methylene blue adsorption effect is best,and adsorption effect is caused by the positive and negative charges.In EF3 recycling studies,methylene blue solution unit capable and removal efficiency of EF3 increased with the increase of frequency,the downward trend was presented.And tne lignin can be used to seven times.Lignin fractionation and recycling process is sustainable,and in accordance with the requirements of green environment.The lignin is renewable.And the solutions(glycerol,ethanol and water)used in fractionation and recycling are green solvents utilized as the green solvents.Therefore,in this study,the material,method and recycling are green and sustainable.